1. Field of the Invention
The present invention relates to a semiconductor device provided with a semiconductor sensor chip including a structural member which is displaced in accordance with physical quantity applied thereto in order to detect the physical quantity such as acceleration and yaw rate, and a manufacturing method thereof.
2. Description of Related Art
For example, an electrostatic capacity type semiconductor acceleration sensor is provided with a beam structure which is displaced in response to an acceleration applied thereto. A sensor chip provided with a sensing portion including the beam structure is manufactured by use of a surface micro machining technique applied to semiconductor materials. Because the semiconductor acceleration sensor as described above is easily miniaturized and has good consistency with a semiconductor manufacturing process, the sensing portion and a sensor circuit for carrying out control of the sensing portion and processing of sensor outputs are formed together in a common semiconductor chip.
As a form of a package to house such a semiconductor acceleration sensor, a resin-molded package is most suitable to reduce the cost of production. However, when the resin-molded package is adopted, it is necessary to protect the beam structure having a small mechanical strength from pressure of molding resin. For this reason, conventionally, a protecting cap is provided on the semiconductor chip so as to cover the sensing portion and the sensor circuit.
In recent years, an acceleration sensor utilized in an air-bag system or a suspension control system of a vehicle is required to achieve miniaturization and low manufacturing cost. However, in a conventional arrangement in which the sensing portion and the sensor circuit stand in a single plane on the common semiconductor chip and the protecting cap is provided thereabove, it is difficult to meet the requirement of miniaturization and low cost. That is, in a conventional semiconductor acceleration sensor, not only the chip size thereof is two-dimensionally enlarged but also it is necessary to provide the protecting cap separately. Therefore, miniaturization of the sensor is very difficult. Further, because the chip size is two-dimensionally enlarged, the number of sensor chips taken from a single wafer is reduced. Furthermore, because the sensing portion and the sensor circuit are formed on the common chip, the number of steps in manufacturing process performed to the common chip is increased and a yield factor of the sensor chip is thereby decreased. As a result, the manufacturing cost of the sensor chip rises. This tendency becomes significant as a degree of integration and an area of the sensor circuit becomes large.
Also, as disclosed in Japanese Patent Application Laid-Open No. H.6-347475, there is a semiconductor sensor in which a sensor chip is disposed on a glass substrate and a protecting cover formed from a silicon plate provided with a signal processing circuit and a concave portion for housing the sensor chip is placed to cover the sensor chip. Due to such a structure, the semiconductor sensor can withstand molding resin.
However, in such a semiconductor sensor as well, because the sensor chip and the signal processing circuit are two-dimensionally arranged and the protecting cover is separately provided, the size thereof is enlarged in two-dimension. As a result, it is difficult to achieve miniaturization of the sensor as a whole. Further, because the glass substrate and the protecting cover (silicon plate) are bonded by anodic junction, a condition of air tightness may be insufficient. Furthermore, because a pulling-out electrode from the signal processing circuit is physically contacted with a pulling-out electrode from the glass substrate to connect them each other, contact resistance between the pulling-out electrodes may be increased. As a result, the reliability of operation of the sensor is low.